1. Field of the Invention
The present invention relates to a thermosensitive recording material capable of producing images with improved preservability and reliability.
2. Discussion of Background
There is conventionally known a thermosensitive recording material comprising a support and a thermosensitive recording layer formed thereon, comprising as the main components an electron-donor type colorless or light-colored dye precursor and an electron-acceptor type color developer. Colored images are obtained in the above-mentioned thermosensitive recording material in such a manner that the dye precursor is allowed to react with the color developer instantaneously by the application of heat to the thermosensitive recording layer using a thermal head, a thermal pen, laser beam or the like. Such a recording material has become the mainstream in this field, and the basic technique of this art is disclosed in Japanese Patent Publications 43-4160, 45-14039 and the like.
The thermosensitive recording material of this kind is widely utilized as a recording material for use with facsimile machines, label printers, and ticket vendors because of the following advantages over other conventional recording materials:
(1) images can be recorded by using a relatively simple device,
(2) the maintenance of the device is easy,
(3) images can be recorded without generating noise, and
(4) the thermal coloring sensitivity is excellent and the coloring density of obtained images is high.
However, since this type of thermosensitive recording material utilizes the reversible reaction of the leuco dye, the thermosensitive recording material has the shortcomings that recorded images is fading away with time while allowed to stand for a long period of time, or become decolorized when the recorded images come into contact with chemicals, oils and water or exposed to light. Although various proposals are made to solve the aforementioned problems, all the problems are not completely solved.
As the thermosensitive recording material utilizing a nonreversible reaction, a thermosensitive recording material comprising an organic reducing agent or chelating agent as an electron-donor and a metallic salt of an organic acid as an electron-acceptor is proposed as disclosed in Japanese Patent Publications 32-8787 and 34-6485; a thermosensitive recording material comprising an imino compound and an isocyanate compound is proposed as in Japanese Laid-Open Patent Applications 58-38733 and 58-54085; and a thermosensitive recording material comprising an aromatic aldehyde compound, an organic condensation product containing --NH.sub.2 group or &gt;NH group, and an electrophilic color developer is proposed as in Japanese Laid-Open Patent Application 4-221675. These nonreversible thermosensitive recording materials have the shortcomings that the background area is colored and the fogging readily takes place although the images recorded in these recording materials have good stability.